1. Field of the Invention
The present invention relates to a method of measuring a hematocrit value of the blood, and separately sampling the plasma (or serum) and the blood cells (or blood clots), after separating blood into plasma and blood cells.
2. Description of the Related Art
The hematocrit value (to be referred to as an Ht value hereinafter) means a volume ratio of a blood cell component in blood. In general, the Ht value is represented by a ratio of a height of a settled blood cell component with respect to a total height of blood in a glass tube in which blood added with an anticoagulant is separated into a plasma component and a blood cell component. This value is an effective scale for checking whether blood is normal. Therefore, the Ht value is not only effective data for checking a human health condition but also essential data for checking whether blood is transfusable to patients. For this reason. Ht value measurement of blood from a donor is always performed upon blood transfusion. Separated plasma and blood cell components are sampled from a blood sample subjected to the Ht value measurement and used in various pathologic and compatibility tests.
The Ht value must be measured to assure safety of both a blood donor and a blood acceptor. For example, if the Ht value of a donor's blood is lower than a predetermined level, blood collection may cause anemia. Therefore, if the Ht value is significantly low, blood collection must be avoided. On the other hand, if the Ht value is abnormally high or low, an influence on a blood acceptor cannot be also neglected. Therefore, any use of such blood must be made very carefully or avoided in some cases.
The following methods and apparatus for measuring an Ht value and separately sampling a plasma component have been conventionally known.
An Ht measuring method is disclosed in Japanese Patent Disclosure (Kokai) No. 60-93348. In this method, blood added with an anticoagulant is centrifugally separated in a glass capillary and irradiated with collimated light, and the amount of light transmitted through the capillary is measured by a plurality of light-receiving elements. A transmitted light amount at a plasma portion is naturally larger than that at a blood cell portion. Therefore, the lengths of the plasma and blood cell portions are determined in accordance with a transmitted light amount detected by each light-receiving element, and the Ht value is calculated on the basis of the determined lengths and output to a suitable display unit such as a printer.
An apparatus for sampling a serum component is disclosed in Japanese Patent Disclosure (Kokai) No. 62-269037. By using this apparatus, serum can be separately sampled in an efficient manner from blood having a known Ht value as follows. That is, blood is separated into serum and blood clots in a collection tube. A suction nozzle located at a predetermined height from the bottom surface cf the blood collection tube is gradually descended at a predetermined rate. When the distal end of the suction nozzle reaches the surface of the serum layer, the serum is sucked from the suction nozzle and flowed through a duct connected to the nozzle. The duct includes a detection electrode. When the electrode detects a flow of the serum, it is determined that the suction nozzle reaches the serum surface. Therefore, by calculating a descent distance in accordance with a descent rate of the nozzle and a time interval from a timing at which the suction nozzle starts descent to a timing at which a detection signal is obtained, the height of the serum surface can be obtained. By multiplying the height of the serum surface by the known Ht value, the bottom surface height of a serum layer can be obtained. As a result, a descent distance of the suction nozzle can be determined, and the serum can be separately sampled efficiently.
The above conventional techniques have the following drawbacks.
That is, in both of the above conventional techniques, only either Ht value measurement or serum sampling can be performed. Therefore, since Ht measurement and serum sampling must be independently performed, a considerably long time is required.